Actuation lockout for a surgical instrument

ABSTRACT

Embodiments of a surgical instrument including an actuation lockout system as well as its method of use are disclosed. In one embodiment, a surgical instrument includes a trigger and a driveshaft coupled to the trigger such that actuation of the trigger causes the driveshaft to move from a first position to a second position, thereby resulting in deployment of a surgical fastener. An actuation lockout system restrains distal movement of the driveshaft until a force greater than or equal to a threshold force is applied to the trigger.

FIELD

Disclosed embodiments are related to actuation lockouts for surgicalinstruments.

BACKGROUND

Oftentimes a surgical mesh fabric or other prosthetic repair fabric isused during a surgical repair of a hernia or other tissue defect. Theprosthetic repair fabric may be placed in an open procedure orlaparoscopically. To secure the repair fabric in place, one or morefasteners may be deployed through the prosthetic repair fabric and intothe underlying tissue.

SUMMARY

In one embodiment, a surgical instrument includes a power transmissionincluding a trigger and a driveshaft operatively coupled to the trigger.Actuation of the trigger moves the driveshaft between at least a firstposition and a second position. The surgical instrument further includesan actuation lockout system operatively associated with the powertransmission. The actuation lockout system substantially preventsmovement of the driveshaft from the first position to the secondposition until a force greater than or equal to a threshold force isapplied to the trigger.

In another embodiment, a surgical instrument includes a powertransmission including and a driveshaft operatively coupled to thetrigger. Actuation of the trigger moves the driveshaft between at leasta first position and a second position. The surgical instrument furtherincludes a first camming surface associated with a portion of the powertransmission and a second camming surface arranged to block movement ofthe first camming surface in a locked configuration, and permit movementof the first camming surface in an unlocked configuration. A biasingmember is operatively coupled to at least one of the first cammingsurface and second camming surface. The biasing member urges the cammingsurfaces into the locked configuration. An actuation force greater thanor equal to a threshold force applied to the trigger moves the firstcamming surface and the second camming surface to the unlockedconfiguration.

In yet another embodiment, a method of operating a surgical instrumentincludes initially restraining movement of a driveshaft operativelyassociated with a trigger using an actuation lockout system. The methodfurther includes applying a force greater than or equal to a thresholdforce to a trigger of the surgical instrument to move an actuationlockout system from a locked configuration to an unlocked configuration,and displacing the driveshaft from a first position to a second positionwhen the actuation lockout system is in the unlocked configuration.

It should be appreciated that the foregoing concepts, and additionalconcepts discussed below, may be arranged in any suitable combination,as the present disclosure is not limited in this respect. Further, otheradvantages and novel features of the present disclosure can be morefully understood from the following description in conjunction with theaccompanying drawings.

In cases where the present specification and a document incorporated byreference include conflicting and/or inconsistent disclosure, thepresent specification shall control.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 is a cross-sectional view of a surgical instrument incorporatingan actuation lockout system;

FIG. 2 is a perspective view of one embodiment of an actuation lockoutsystem;

FIG. 3 is an exploded perspective view of the actuation lockout systemof FIG. 2;

FIG. 4A is a side view of one embodiment of a surgical instrumentincorporating an actuation lockout system in a locked configuration;

FIG. 4B is a side view the actuation lockout system of FIG. 4A in anunlocked configuration;

FIG. 4C is a cross-sectional view of a surgical instrument including theactuation lockout system of FIG. 4A during actuation; and

FIG. 5 is a side view of one embodiment of an actuation lockout systemand a power assist device associated with a driveshaft.

DETAILED DESCRIPTION

The inventors have recognized issues associated with slow, partial,and/or unintentional actuations of a surgical instrument. Consequently,the inventors have realized the benefits associated with providing anactuation lockout system that restrains actuation of a surgicalinstrument until a threshold force is applied to an actuation trigger.Without wishing to be bound by theory, in some instances when a userovercomes the threshold force to actuate the surgical instrument, it mayresult in the user naturally completing a full actuation of the surgicalinstrument while avoiding a slow, partial, and/or unintentionalactuation though other benefits may also result from such an instrumentas the disclosure is not so limited.

In some embodiments, a surgical instrument includes a power transmissionincluding a trigger operatively coupled to a drive shaft. The powertransmission transfers force applied to the trigger by a user to thedriveshaft which is constructed and arranged to deploy a fastener from adistal end of the surgical instrument. The surgical instrument may alsoinclude an actuation lockout system associated with any portion of thepower transmission including the trigger, driveshaft, and/or anyintermediate component to prevent actuation of the surgical instrumentuntil a threshold force is applied to the trigger. Components that maybe included in a power transmission between the trigger and driveshaftinclude spur gears, helical gears, crown gears, worm gears, planetarygear systems, belts, clutch interfaces, linkages, or any otherappropriate component capable of transmitting power from one componentto another. However, embodiments in which the trigger is directlycoupled to the driveshaft are also contemplated. Further, it should beunderstood that the driveshaft may be configured to deploy anyappropriate type of fastener including both linearly or rotationallydeployed fasteners. Consequently, it should be understood that the powertransmission and driveshaft may provide a linear or rotational force toan associated fastener when the trigger is actuated. Various embodimentsof specific actuation lockout systems are described in more detailbelow.

It should be understood that the current disclosure is not limited toany particular displacement direction of the driveshaft. For example, insome embodiments, the driveshaft may be displaced axially, rotationally,or in any other appropriate fashion. Further, the actuation lockoutsystem may be constructed and arranged in any suitable manner tofacilitate restraining displacement of the driveshaft in any suitabledirection until a force greater than or equal to a threshold force isapplied to the trigger.

Depending on the particular embodiment, the threshold force required totransition the actuation lockout system from a locked configuration inwhich actuation of the surgical instrument is restrained, to an unlockedconfiguration in which actuation of the surgical instrument is notrestrained, may be larger than or equal to a force required to actuatethe surgical instrument to deploy a surgical fastener or accomplishanother action via actuation of the trigger such as cutting, suturing,as well as staple deployment to name a few. Therefore, application ofthe threshold force to the trigger and subsequent transitioning of theactuation lockout system from the locked configuration to the unlockedconfiguration may result in a user naturally completing full actuationof the trigger because they are already applying a force greater than orequal to the actuation force. This may substantially prevent slow and/orincomplete deployment of a surgical fastener when used in a surgicalfastening instrument. While the threshold force may be greater than orequal to the actuation force in some embodiments, it should beunderstood that in other embodiments, the threshold force may be lessthan or equal to the actuation force as the disclosure is not solimited.

It should be understood that an actuation lockout out may have anyappropriate force threshold for actuation. For example, the thresholdforce may be greater than or equal to about 0.25 pounds, 0.5 pounds, 1pound, 2 pounds, or any other appropriate force. Correspondingly, thethreshold force may be less than or equal to about 5 pounds, 4 pounds, 3pounds, 2 pounds, 1 pound, or any other appropriate force. Variouscombinations of the above threshold force limits are contemplatedincluding a threshold force between or equal to about 0.5 pounds to 1pound, 1 pound to 5 pounds, or any other combination.

Similar to the above, it should be understood that an actuation forcefor deploying a fastener may be any appropriate force as the disclosureis not so limited. For instance, the actuation force may be greater thanor equal to about 0.25 pounds, 0.5 pounds, 1 pound, 2 pounds, or anyother appropriate force. Correspondingly, the threshold force may beless than or equal to about 4 pounds, 3 pounds, 2 pounds, 1 pound, orany other appropriate force. Various combinations of the above thresholdforce limits are contemplated including a threshold force between orequal to about 0.5 pounds to 1 pound, 1 pound to 4 pounds, or any othercombination.

In one embodiment, actuation of a driveshaft to deploy a surgicalfastener involves moving the driveshaft from a first position to asecond position. Depending on whether a linearly or rotationallydeployed fastener is used, the driveshaft displacement may involveeither a first and second rotational position or a first proximallongitudinal position and a second distal longitudinal position. Ineither case, an actuation lockout system associated with a powertransmission including the driveshaft is configured to restrain movementof the driveshaft from the first position to the second position until athreshold force is applied to a trigger operatively coupled to thedriveshaft. During actuation, the actuation lockout system may betransitioned between a locked configuration in which motion of thedriveshaft is restrained, and an unlocked configuration in which thedriveshaft is permitted to move. The actuation lockout systemtransitions from the locked configuration to the unlocked configurationwhen a force greater than or equal to the threshold force is applied tothe trigger.

Depending on the embodiment, an actuation lockout system may be movedbetween locked and unlocked configurations in any number of ways. In oneembodiment, an actuation lockout system is movable between the lockedand unlocked configuration using a suitable arrangement of two or morecorresponding surfaces disposed on various portions of the powertransmission and/or surgical instrument. For example, in one embodiment,an actuation lockout system includes a first surface directly, orindirectly, coupled to the driveshaft and a second surface directly, orindirectly, coupled to the handle or other portion of a surgicalinstrument that is arranged to selectively block movement of the firstsurface. When the actuation lockout system is in the lockedconfiguration, the second surface is engaged with the first surface suchthat displacement of the first surface, and therefore the driveshaft,which is operatively coupled to the first surface, is restricted.Correspondingly, when the actuation lockout system is in the unlockedconfiguration, the first and second surfaces are disengaged, separated,or otherwise configured to allow the first surface, and the associateddriveshaft, to freely move relative to the second surface. Specificembodiments of arrangements of the first and second surfaces aredetailed further below.

In certain embodiments, engaging surfaces arranged to selectivelyprevent actuation of a surgical instrument form a camming arrangementsuch that the surfaces are urged from a locked configuration to anunlocked configuration when a sufficient force is applied to actuate thedriveshaft. Such a camming arrangement may be desirable to provide asimple actuation lockout system which automatically moves from thelocked configuration to the unlocked configuration during actuation ofthe driveshaft from a first position to a second position. For example,a first camming surface associated with the driveshaft may be engagedwith a second camming surface associated with a handled of a surgicalinstrument when an actuation lockout system is in a lockedconfiguration. The camming surfaces may be configured such that a forceapplied to actuate the driveshaft causes the first camming surface toapply a force to the second camming surface that displaces the secondcamming surface to the unlocked configuration, thereby allowing relativemovement of the first and second surfaces and thus actuation of thedriveshaft.

The various embodiments of an actuation lockout system disclosed hereinare not limited to any particular type of fastener or surgicalinstrument. For example, an actuation lockout system could be used witha tack, clip, staple, pin, tissue anchor, bone anchor, coil fasteners,screw fasteners, and any other type of fastener that could benefit fromthe use of an actuation lockout system to avoid incomplete and/orunintentional deployment of a fastener. Similarly, the actuation lockoutsystem may be used in any number of medical procedures including, butnot limited to, attaching a repair fabric or mesh to underlying tissue,attaching adjacent layers of tissue, attaching identification devicesand/or tags to livestock, and other appropriate applications involvingthe deployment of a fastener.

For the sake of clarity, the currently disclosed embodiments aredirected to laparoscopic fastening devices. However, the currentdisclosure is not so limited. Instead, the actuation lockout systemcould be incorporated in any actuated surgical instrument. For example,an actuation lockout system could be employed in an endoscopic device, aborescopic device, a catheter, a surgical instrument for use in “open”procedures, surgical instruments including actuated working tools, orany other appropriate surgical instrument. In embodiments where thesurgical instrument deploys fasteners, the surgical instrument may beconstructed to allow the user to load the instrument with one or morefasteners, be preloaded with one or more fasteners, be selectivelyconnected with a disposable loading unit including one or more preloadedfasteners, or be constructed in any other appropriate manner.

Turning now to the figures, specific non-limiting embodiments ofactuation lockout systems and surgical instruments are described.

FIG. 1 depicts a surgical instrument 10 including a handle 12 and ahollow elongated shaft 14 extending from the handle towards a distal endof the device from which fasteners are deployed. The surgical instrumenthas a power transmission including a trigger 16, a transmission linkage18, a shuttle 20, and a driveshaft 24. The trigger is coupled to thetransmission linkage, which is operatively coupled to the shuttle, whichis in turn coupled to the driveshaft. Thus, when the trigger isactuated, the transmission linkage displaces the shuttle and associateddriveshaft in a distal direction. The driveshaft is configured andarranged to apply a force to a distally located fastener, eitherdirectly or indirectly, to deploy the fastener from the surgicalinstrument. When released, the trigger is returned to an initialposition by a return spring 22. This, in turn, returns the shuttle anddriveshaft to their initial positions. Thus, actuation of the triggerreciprocates the shuttle and driveshaft between distal and proximalpositions. While a specific linkage and trigger mechanism are depictedin the figure, different triggers and transmission linkages areenvisioned. For example, a transmission linkage may incorporate gears,multi-bar linkages, or any other appropriate transmission mechanisms.Also, in some embodiments, the transmission linkage, or other powertransmission component, is constructed to provide a mechanical advantagefor displacing the shuttle.

FIGS. 1-4 also illustrate an embodiment of an actuation lockout system50 that may be included in a surgical instrument. In the depictedembodiment, the actuation lockout system includes a first cammingsurface 52 disposed on the shuttle 20, and a second camming surface 54disposed on an arm 56. The arm is rotatable about an axle 60 associatedwith the handle 12. A biasing member 58 is operatively coupled to thearm. In the depicted embodiment, the biasing member is a torsion spring.However, other types of biasing members may be suitable, as describedbelow. The biasing member biases the arm such that the second cammingsurface is urged toward the first camming surface. This arrangementresists the force applied to the second camming surface by the firstcamming surface when the shuttle is actuated by the trigger 16. Thisresistance to movement provides a threshold force which must be overcometo move the actuation lockout system from the locked configuration tothe unlocked configuration. As the force applied to the triggerincreases, the force applied to the second camming surface by the firstcamming surface also increases until it meets or exceeds the resistingforce provided by the biasing member. Once the threshold force is met orexceeded, the first camming surface displaces the second camming surfaceto permit distal motion of the shuttle and the driveshaft.

In view of the above, the actuation lockout system is movable between alocked configuration (FIG. 4A), and an unlocked configuration (FIG. 4B).In the locked configuration, the first and second camming surfaces arein contact with one another, thus restricting distal movement of theshuttle. In the unlocked configuration, the second camming surface hasbeen cammed out of the path of travel of the first camming surface by anapplied actuation force, thus removing the restraint from the shuttle,and permitting the shuttle and associated driveshaft to move distally todeploy a fastener, as described above. Although in the depictedembodiment, the first and second surfaces are disposed on the shuttleand the arm, respectively, other arrangements are envisioned. Forexample, the first and second camming surfaces may be disposed on anysuitable part of the surgical instrument such as the handle, or on anypart of the power transmission including the driveshaft, thetransmission linkage, or the trigger.

As best illustrated by the embodiment depicted in FIG. 4C, the cammingsurfaces 52 and 54 may be configured such that distal movement of theshuttle 20 causes the first camming surface to apply a camming force Cto the second camming surface in a direction transverse to both alongitudinal axis of the driveshaft and a direction of movement of theshuttle. This force displaces the second camming surface out of the pathof movement of the first camming surface which places the actuationlockout system in the unlocked configuration. In the depictedembodiment, this displacement is embodied by rotation of the arm 56about axle 60. While an embodiment has been described where an armrotates to move to the unlocked position, it should be understood thatthe arm, or other appropriate locking member, may also be moved in anyappropriate manner including linearly in response to interaction of thecamming surfaces to selectively lock actuation of a surgical instrument.For example, a camming surface may be connected to a linearly expandingspring, such as a coil spring, such that it is displaced transverse to apath of movement of the corresponding camming surface instead ofrotating out of the way.

It should be understood that camming surfaces used in an actuationlockout system may have any suitable shape and/or configuration. Forexample, in the depicted embodiment, the first camming surface is aconcave curved surface formed on the shuttle 20. The curve may have anysuitable radius, and the radius may be constant, or may be differentalong different points of the curve to provide a desired actuation forceprofile. Correspondingly, in some embodiments, the use of a rollingcamming surface may be desirable to provide easier and/or smootheroperation of the camming interface. One such embodiment is a cylindricalroller 62 as depicted in the figures. In the depicted embodiment, theradius of the roller generally complements the curvature of the firstcamming surface. However, embodiments in which the curvatures, or othershape, of the camming surfaces do not complement each other are alsocontemplated. The roller includes a through hole in which a roller axle64 is received in through holes 66 formed in tabs 56 a extending fromarm 56. In some embodiments, the roller 62 may include bearings, such asball bearings or roller bearings, to further facilitate rotation of theroller on the roller axle. Alternatively, a roller may not include abearing, and may instead feature a suitable clearance around an axle tofacilitate rotation. In other embodiments, the second camming surface 54may not rotate, and instead may simply slide relative to the firstcamming surface 52. Furthermore, it should be understood that the firstand/or second camming surfaces may not include any curvature; forexample, flat angled camming surfaces may be suitable in someembodiments.

Having described the various components of a power transmission andactuation lockout system included in a surgical instrument, their methodof operation is described in more detail with reference to FIGS. 4A-4C.FIGS. 4A and 4C depict the actuation lockout system in the lockedconfiguration. The camming surfaces 52 and 54 are engaged to restraindistal motion of the shuttle 20 and associated driveshaft 24. Biasingmember 58 biases arm 56 in direction A urging the camming surfacestogether, as described above. When a force is applied to trigger 16,rotation of the trigger in direction T applies a force to the shuttle 20via linkage 18 in a distally oriented direction S. The force indirection S then produces a camming force on arm 56 in direction C awayfrom the path of movement of the shuttle due to the camming arrangementof surfaces 52 and 54. While another force component is also applied inthe distal direction by the camming arrangement, this component of theapplied force has not been illustrated in the figure for clarity. Asdepicted in FIG. 4C, the camming force applied in direction C to thesecond camming surface opposes at least a portion of the force appliedby the biasing member in rotational direction A. When the force appliedto the trigger exceeds a threshold force, the force along direction C isequal to or greater than the opposing force applied by the biasingmember. Once this occurs, the second camming surface is displaced out ofthe path of the shuttle and first camming surface placing the actuationlockout system in the unlocked configuration, as shown in FIG. 4B. Inthe unlocked configuration, the shuttle 20 and driveshaft 24 aredisplaced distally along direction S in order to deploy a surgicalfastener, as described above.

In the depicted embodiment, the shuttle 20 further includes a surface 66on which the second camming surface 54 travels when the actuationlockout system 50 is in the unlocked configuration. Specifically,surface 66 includes a slope which allows the force in the biasing member58 to decrease as the shuttle moves distally. The slope of the surfacemay be chosen such that the force provided by return spring 22 issufficient to urge the actuation lockout system back into the lockedconfiguration after a surgical fastener is deployed and a force appliedby a user to the trigger 16 is removed. In some embodiments, the surfacemay act as a third camming surface which interacts with the secondcamming surface to provide additional force to the shuttle or driveshaftin the distally oriented direction S due to the force applied by thebiasing member. Such a configuration may further promote completeactuation of the surgical instrument when the actuation lockout systemmoves from the locked configuration to the unlocked configuration.However, it should be understood that surface 66 may simply be flat, maynot act as a camming surface, may be curved, or have any other suitableshape and/or configuration for accommodating the second camming surfaceas the shuttle is displaced, as the disclosure is not so limited.

While the first camming surface has been depicted on the shuttle, thecurrent disclosure of an actuation lockout system is not so limited.Therefore, it should be understood the first camming surface may bedisposed on the driveshaft, a component coupled to the driveshaft, thetrigger, or any other appropriate portion of the power transmissionsystem such that actuation of the trigger displaces the camming surfacesrelative to each other to selectively permit actuation of the driveshaftonce a threshold force has been applied to the trigger. For example, inone embodiment, a camming surface may be arranged coaxially with thedriveshaft. Furthermore, although in the depicted embodiment, theactuation lockout system is disposed on one side of the shuttle, inother embodiments, portions of an actuation lockout system may beprovided on either or both sides of the shuttle, or it may not beassociated with the shuttle at all.

Although the use of complementary camming surfaces is depicted in thefigures to move the actuation lockout system from the lockedconfiguration to the unlocked configuration, other arrangements andmechanisms are also contemplated. For example, the actuation lockoutsystem may include a rack and pinion arrangement such as a pinion gearcoupled to the trigger and rack formed on surface arranged to limitactuation. Actuation of the trigger may rotate the pinion and in turndrive a displacement of the rack and the associated surface towards theunlocked configuration. Alternatively, linkages coupled to the triggermay be arranged to displace a locking mechanism. In another example, acamming surface may be disposed on ratchet and pawl arrangement whichselectively locks the actuation lockout system. The camming surface maymove the pawl over a tooth or similar feature on the ratchet when athreshold force is applied to the camming surface in order to move theratchet and pawl to an unlocked configuration. In further examples, anactuation lockout system may include complementary surfaces which may beselectively engaged to form an interference fit, a latch which isconfigured to release above a predetermined threshold force, or anyother suitable mechanism or arrangement, as the disclosure is not solimited. A locking mechanism may include a catch, latch, clasp, adeadbolt, a hook and eye, or any other suitable arrangement. Aninterference fit between complementary surfaces may provide a frictionalresistance force; the resistance force may provide the threshold forcewhich must be overcome to move the actuation lockout system to theunlocked configuration. In view of the above, it should be understoodthat an actuation lockout system may include any suitable arrangement ofcomponents which restricts relative motion of two or more componentsalong at least one direction when in a locked configuration.Furthermore, an actuation lockout system may include any suitablemechanism to move the actuation lockout system between the locked andunlocked configurations; such mechanisms may or may not be coupled to atrigger of a surgical instrument.

As described above, in some embodiments, an actuation lockout systemincludes a biasing member coupled to at least one camming surface toapply a locking force and selectively prevent actuation of the surgicalinstrument. However, it should be understood that embodiments that donot include a biasing member are also contemplated as the disclosure isnot so limited. For example, a frictional interface, a particular shapeand/or configuration of surfaces, or any other suitable arrangement maybe used to provide a threshold actuation force for unlocking theactuation lockout system as the disclosure is not so limited.

While a torsion spring has been illustrated for the biasing member, thebiasing member is not limited to only a torsion spring. For example, thebiasing member may include, but is not limited to, a coil spring, a leafspring, a magazine spring, a gas spring, an elastic rod, or any othersuitable structure or device capable of providing a force to resistdisplacement of the second camming surface and provide a threshold forcefor selectively unlocking the actuation lockout system. Additionally,while a separate biasing member has been depicted, a biasing member mayalso be integrally formed with a portion of the actuation lockoutsystem. For example, an integrally formed feature such as a flexiblearm, tab, or other feature may function as both a camming surface andbiasing member as the disclosure is not so limited.

In certain embodiments, an actuation lockout may be particularly usefulwhen incorporated in a surgical instrument with a power assist deviceconfigured to aid in deploying a surgical fastener. The power assistdevice may be configured to provide a short duration impulse to thedriveshaft by striking the driveshaft with a moving mass, as describedin more detail below. Without wishing to be bound by theory, providing ashort duration impulse may result in a larger force being applied to afastener during deployment, which may improve prosthetic fabricpenetration and reduce the required manual force input from a user.Depending on the particular embodiment, a power assist device may beactuated when a threshold force is applied to the trigger and anactuation lockout system is moved from a locked configuration to anunlocked configuration.

One embodiment of a power assist device is depicted in FIGS. 1 and 5.The depicted power assist device includes an energy storage member 28, astriker 30, and an impact surface 32. In the depicted embodiment, theimpact surface 32 is a collar coupled to the driveshaft 24, though otherarrangements are also contemplated. The power assist device alsoincludes an energy storage member housing 26 and a locking mechanism 34.As depicted in the figures, the energy storage member is a coil spring.However, the energy storage member may be any appropriate componentcapable of storing and releasing energy including coil springs, airsprings, gas springs, elastic rods or bands, magazine springs, leafsprings, torsion bars, or torsion springs. Further, the energy storagemember housing is operatively coupled to the shuttle 20. The energystorage member is coaxially disposed on the driveshaft 24 and partiallydisposed within an interior volume of the energy storage member housing.However, other configurations including ones where the energy storagemember is disposed outside of the housing are also contemplated. Theenergy storage member and energy storage member housing are configuredsuch that displacing the driveshaft in the distal direction displacesthe energy storage member housing and associated proximal end of theenergy storage member in the distal direction as well. Since the energystorage member 28 is located between the striker and energy storagemember housing while the striker is locked in place by the lockingmechanism 34, this movement compresses the energy storage member.

As the driveshaft continues to be displaced in the distal direction, thelocking mechanism 34 is moved to the unlocked position through the useof a first power assist camming surface 38 located on the energy storagemember housing 26 and a second power assist camming surface 36 locatedon the locking mechanism. As the energy storage member housing 26 isdisplaced in the distal direction, the first power assist cammingsurface comes into contact with the second power assist camming surfaceand displaces the locking mechanism outwards to release the striker 30and the energy storage member 28. The released energy storage memberaccelerates the striker in the distal direction towards the impactsurface 32 to impart an impulse to the driveshaft 24 and deploy anassociated fastener. Upon being struck, the driveshaft accelerates in adistal direction to deploy a fastener.

While one particular power assist device has been described herein,other suitable embodiments, arrangements, and/or configurations of apower assist device for use in a surgical instrument are also describedin U.S. patent application Ser. No. 13/804,043 filed on Mar. 14, 2013,published as US 2014/0276963, the disclosure of which is herebyincorporated by reference in its entirety.

While the present teachings have been described in conjunction withvarious embodiments and examples, it is not intended that the presentteachings be limited to such embodiments or examples. On the contrary,the present teachings encompass various alternatives, modifications, andequivalents, as will be appreciated by those of skill in the art.Accordingly, the foregoing description and drawings are by way ofexample only.

What is claimed is:
 1. A surgical instrument comprising: a powertransmission including a trigger and a driveshaft operatively coupled tothe trigger, wherein actuation of the trigger moves the driveshaftbetween at least a first position and a second position; and anactuation lockout system operatively associated with the powertransmission, wherein the actuation lockout system prevents movement ofthe driveshaft from the first position to the second position until aforce greater than or equal to a threshold force is applied to thetrigger.
 2. The surgical instrument of claim 1, wherein the firstposition is a proximal position and the second position is a distalposition.
 3. The surgical instrument of claim 1, wherein the firstposition is a first rotational position and the second position is asecond rotational positions.
 4. The surgical instrument of claim 1,wherein the actuation lockout system comprises a first camming surfaceassociated with the driveshaft, and a second camming surface arranged toselectively block movement of the first camming surface.
 5. The surgicalinstrument of claim 4, further comprising a biasing member operativelycoupled to at least one of the first camming surface and second cammingsurface.
 6. The surgical instrument of claim 5, wherein the biasingmember is at least one of a torsion spring, a coil spring, a leafspring, a magazine spring, a gas spring, and an elastic rod.
 7. Thesurgical instrument of claim 4, wherein the first and second cammingsurfaces have complementary shapes.
 8. The surgical instrument of claim4, wherein at least one of the first camming surface and second cammingsurface has a curved shape.
 9. The surgical instrument of claim 4,wherein at least one of the first camming surface and the second cammingsurface is a roller.
 10. A surgical instrument comprising: a powertransmission including a trigger and a driveshaft operatively coupled tothe trigger, wherein actuation of the trigger moves the driveshaftbetween at least a first position and a second position; a first cammingsurface associated with a portion of the power transmission; a secondcamming surface arranged to block movement of the first camming surfacein a locked configuration and permit movement of the first cammingsurface in an unlocked configuration; and a biasing member operativelycoupled to at least one of the first camming surface and the secondcamming surface, wherein the biasing member urges the camming surfacesinto the locked configuration, and wherein an actuation force greaterthan or equal to a threshold force applied to the trigger moves thefirst camming surface and the second camming surface to the unlockedconfiguration.
 11. The surgical instrument of claim 10, furthercomprising a handle, wherein the second camming surface is associatedwith the handle.
 12. The surgical instrument of claim 10, wherein atleast one of the first camming surface and the second camming surfaceincludes at least a portion of a rotatable arm.
 13. The surgicalinstrument of claim 10, wherein at least one of the first cammingsurface and the second camming surface include a roller.
 14. Thesurgical instrument of claim 10, wherein the first and second cammingsurfaces have complementary shapes.
 15. The surgical instrument of claim10, wherein at least one of the first camming surface and the secondcamming surface has a curved shape.
 16. The surgical instrument of claim10, wherein the first position is a proximal position and the secondposition is a distal position.
 17. The surgical instrument of claim 10,wherein the first position is a first rotational position and the secondposition is a second rotational positions.
 18. The surgical instrumentof claim 10, wherein the biasing member is at least one of a torsionspring, a coil spring, a leaf spring, a magazine spring, a gas spring,and an elastic rod.
 19. A method of operating a surgical instrument, themethod comprising: initially restraining movement of a driveshaftoperatively associated with a trigger using an actuation lockout system;applying a force greater than or equal to a threshold force to thetrigger of the surgical instrument to move the actuation lockout systemfrom a locked configuration to an unlocked configuration; and displacingthe driveshaft from a first position to a second position when theactuation lockout system is in the unlocked configuration.
 20. Themethod of claim 19, wherein the first position is proximal position andthe second position is a distal position.
 21. The method of claim 19,wherein the first position is a first rotational position and the secondposition is a second rotational positions.
 22. The method of claim 19,wherein moving the actuation lockout system to the unlockedconfiguration includes camming a second camming surface out of a path ofmovement of a first camming surface operatively associated with thedriveshaft.